Solution combustion synthesis of FeCr2O4 powders for pigment applications: Effect of fuel type

Solution combustion synthesis of iron chromite was reported using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, as well as glycine, urea, citric acid, and ethylene glycol as fuels. The influence of fuel type on the structure, molecular, microstructure as well as chromatic properties of samples was investigated. The X-ray diffraction (XRD) patterns showed that unlike themodynamical prediction, glycine fuel led to strongest combustion and consequent highest XRD peak intensities and lower lattice parameters. Moreover, the change of fuel type and mixing of fuels affected XRD data. Fourier transform infrared analysis showed that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies by using of fuels with weaker combustion reactions. In addition, scanning electron micrographs showed that different morphologies of FeCr₂O₄ particles were obtained depending on the fuel type and ratios. Energy-dispersive X-ray spectroscopy analysis of the samples showed that oxygen concentration of samples was less than that of stoichiometric ratio of FeCr₂O₄ due to local reducing atmosphere. Furthermore, chromatic properties of the powders showed that the pigment synthesized with glycine fuel has a better and lighter grayish brown color than the other ones and can be used as a suitable industrial candidate to create a brown color in the ceramic glaze.     

Synthesis of (Fe,Cr)2O3 solid solution pigment powders for ink application

Iron chromite pigment was synthesized via solution combustion using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, and glycine, urea, citric acid, and ethylene glycol as fuels. The effect of postheating temperature on the structure, microstructure, and chromatic properties of the synthesized powders was also studied. X-ray diffraction patterns showed that the as-synthesized powders were amorphous to crystalline FeCr₂O₄ phases, depending on fuel type. Moreover, regardless of the fuel type, postheating led to the d-space shift and oxidation and formation of (Fe,Cr)₂O₃ solid solution. Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ solid solution was observed at 500/750°C depending on the dominant phase present in the as-synthesized particles. Fourier transform infrared analysis illustrated a shift in the band position of octahedral M–O and tetrahedral M–O bonds due to the movement of Fe cations and the lattice shrinkage by increasing the postheating temperature. Moreover, scanning electron micrographs showed that Fe_0.7Cr_1.3O₃ semispherical fine particles consisted mainly of porous and spongy FeCr₂O₄ particles due to the oxidation and phase transformation during postheating. According to chromatic measurements, the ink prepared by using the powders synthesized in the presence of glycine and post-heated at 500°C showed reddish-brown color which could be considered a promising candidate for tile decoration application. Furthermore, rheology studies revealed that the prepared ink showed non-Newtonian shear thinning behavior.     

Phase transformation of FeCr2O4 to (Fe,Cr)2O3 solid solution pigment powders: Effect of post-heating temperature

Iron chromite powders were synthesized via solution combustion route using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, as well as glycine–urea, glycine–citric acid, and glycine–ethylene glycol mixtures as fuels. The effect of postheating at different temperatures on the structure, molecular, microstructure, and chromatic properties of powders and tiles colored by in-glaze powders was studied. The X-ray diffraction patterns showed that as-synthesized powders were obtained in crystalline FeCr₂O₄ phases moreover, postheating of the powders led to d-space shift and oxidation and formation of (Fe,Cr)₂O₃ solid solution phase regardless of fuel type. Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ solid solution was observed at 500/750°C depending on the dominant phase of as-synthesized particles. Fourier transform infrared analysis illustrated that the band positions of octahedral M–O and tetrahedral M–O bonds were shifted due to Fe cations movement from their position and lattice shrinkage by increasing of post-heating temperature. Moreover, scanning electron micrographs showed that Fe_0.7Cr_1.3O₃ semispherical fine particles were formed from porous spongy FeCr₂O₄ particles due to oxidation and phase transformation during the postheating. Furthermore, chromatic properties of the samples were represented. The color properties of the pigments showed that the formation of brown pigments is provided with the phase transformation from FeCr₂O₄ to (Fe,Cr)₂O₃ at a temperature of up to 750°C. Moreover, increasing the color purity to this temperature is related to the removal of residual carbonaceous matters. The chromatic properties of the glazed tiles colored using the pigments showed that postheating between 250 and 500°C led to more brown appearance.     

Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

Solution combustion synthesis of CeO2 powders and its application in water treatment

CeO₂ powders were synthesized via a solution combustion method. The product was characterized by X-ray diffraction scanning electron microscope, and BET surface area analysis. The results indicated that the CeO₂ powders present a foaming state with a surface area of 28.17 m² g^–1. The adsorption performance of the CeO₂ powders was tested toward the removal of typical pollutants of Cr(VI) and Congo red (CR). The results showed that the adsorption of Cr(VI) and CR onto CeO₂ powders followed the Langmuir isotherm model and pseudo-second-order kinetics, with an adsorption capacity of 5.69 mg g^–1 and 35.51 mg g^–1, respectively.     

Glycine-assisted solution combustion synthesis of NiCo2O4 electromagnetic wave absorber with wide absorption bandwidth

Design of high-performance electromagnetic (EM) wave absorbing materials has been regarded as an effective solution to excessive EM wave interference problem. As a promising candidate, NiCo₂O₄ absorbers have attracted enormous research attentions. However, currently reported morphology-manipulation synthetic methods of NiCo₂O₄ absorbers are time-consuming and require high energy consumption, which inhibit their practical applications. Herein, a more facile and cost-effective solution combustion synthesis was utilized to fabricate NiCo₂O₄ materials. The absorber prepared by using glycine as fuel displayed the best EM wave absorption performance. Impressively, ultra wide absorption bandwidth of 7.44 GHz from 10.56 GHz to 18 GHz could be achieved with relatively thin thickness of 2.1 mm NiCo₂O₄ sample fabricated in this work displayed the widest effective absorption bandwidth (EAB) among reported NiCo₂O₄-based EM wave absorbing materials so far. In view of its simple and low-cost synthetic process and excellent EM wave dissipation capacity, NiCo₂O₄ samples in this work showed great feasibility as practical absorber. In addition, our findings may also provide new sight for facile preparation of other high-performance EM wave absorbers by solution combustion synthesis instead of complex morphology-manipulation routes.     

Solution combustion synthesis of crystalline V2O3 and amorphous V2O3/C as anode for lithium-ion battery

In this paper, crystalline V₂O₃ and amorphous V₂O₃/C products are synthesized via one-pot solution combustion synthesis (SCS) method (completed within 2 minutes). The characteristics of combustion products could be tuned by changing the amounts of glucose. The as-synthesized crystalline V₂O₃ nanopowder consists of nanoparticles with average size of ~100 nm. Amorphous V₂O₃/C composite exhibits large porous microsheet structure in which oxygen vacancy-enabled amorphous V₂O₃ particles are embedded into N-doped carbon microsheets. The existence of oxygen vacancies can promote energetics for the transport of electrons and ions and maintain the integrity of sample surface morphology. Moreover, N-doping can enhance electrical conductivity and promote the diffusion of electrons and lithium ions. Amorphous V₂O₃/C composite possesses high reversible capacity and superior cycling stability (833 mAh g⁻¹ at 1 A g⁻¹ after 250 cycles, 867 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles), indicating its potential as excellent anode material for lithium-ion battery. The proposed one-step, time- and energy-efficient SCS method has the potential to prepare other oxygen vacancy-enabled transition metal oxides for energy storage.     

Solution combustion synthesis of ZnO powders using CTAB as fuel

Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using cetyltrimethylammonium bromide (CTAB) as fuel. The effects of fuel to oxidant ratios (? = 0.5, 0.75, 1 and 1.5) on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy, and diffuse reflectance spectrometry techniques. The slow decomposition rate of CTAB guaranteed the direct formation of single phase and well-crystalline ZnO powders regardless of fuel content. The specific surface area of the as-combusted ZnO powders with platelet particles increased from 21 ± 1 to 35 ± 2?m²/g with fuel content. The band gap energy also increased from 2.99 to 3.13?eV due to the decrease of particle size. The as-combusted ZnO powders at ? = 1.5 exhibited the highest photodegradation (~69%) of methylene blue under ultraviolet light irradiation, due to their good crystallinity and smaller particle size.     

Novel combustion synthesis of La3+-substituted MnFe2O4

La³⁺-substituted MnFe₂O₄ compounds have been prepared by using a novel combustion synthesis method. This process was found to yield homogeneous, finely crystalline powders without intermediate decomposition and/or calcination steps. Combustion-synthesized powders were sintered at 1000°C, and structural features of thus prepared materials were characterized by XRD analysis and FT-IR spectroscopy. The dc electrical conductivity of synthesized materials has been measured as a function of temperature up to 1000°C. The materials have shown semiconducting behavior at elevated temperatures. The ac electrical conductivity of synthesized samples was found to increase with increasing applied frequency. The dielectric constant and dielectric loss tangent have also been characterized. The article is published in the original.     

Microstructural evolution of supra-nanostructure Al2O3/ZrO2 eutectic powders by combustion synthesis-spray cooling

Eutectic powders with fine microstructure are difficult to synthesize by crushing eutectic bulk because of the damage of crystal structure and the introduction of milling media during preparation process. In this work, a novel combustion synthesis-spray cooling (CSSC) method is developed to fabricate supra-nanostructure Al₂O₃/ZrO₂ eutectic powders. CSSC is a kind of self-heating technique, which simplifies operations, reduces costs and supplies ultra-high cooling rate. The phase composition and the microstructural evolution are investigated using experiment studies and ANSYS simulation. During the process, the t-ZrO₂ are stabilized at room temperature because of the solubility of Al₂O₃ in ZrO₂. The ultra-high cooling rate greatly refined eutectic structure. Although the eutectic structure coarsens with increases in particle size, the interphase spacing of all particles reaches supra nanoscale. The work provides a route for preparing supra-nanostructure Al₂O₃/ZrO₂ eutectic powders and for better understanding the microstructural evolution.     

Solution combustion synthesis of ZnO powders using mixture of fuels in closed system

Single phase ZnO powders with wurtzite structure were synthesized by solution combustion method using various amounts of mixed glycine-citric acid fuel in the presence (open system) and absence (closed system) of air oxygen. Phase evolution, microstructure and optical properties were investigated by thermal analysis, X-ray diffractometry, electron microscopy and Raman, photoluminescence (PL) and diffuse reflectance spectrometry techniques. Rapid combustion reaction in closed system led to weak crystallinity, as confirmed by deep-level emissions in PL spectra. Larger spherical particles (~200?nm) were synthesized in open system at ? =?1. The as-combusted ZnO powders in closed system exhibited higher photocatalytic activity under ultraviolet irradiation, due to their higher adsorption capacity of methylene blue on ZnO surface. Photodegradation rate increased with the increase of fuel content in as-combusted ZnO powders produced by open route as a result of the reduction of particle size and band gap energy.     

Combustion synthesis of ZnAl2O4 powders with tuned surface area

Zinc aluminate powders with tuned surface area were prepared by solution combustion synthesis, using different oxidizer-fuel ratios. As the amount of urea increased, standard heat of reaction and standard Gibbs free energy decreased, whilst adiabatic temperature increased. The larger amount of energy released during combustion facilitated grain growth and sintering, causing the decrease of specific surface area from 156 to 27 m² g⁻¹. The particle size estimated from TEM increased from 8 to 40 nm. The adsorption capacity of zinc aluminate powders with respect to methyl orange was highly dependent on the specific surface area. For an adsorbent dose of 3 g L⁻¹ the removal efficiency of methyl orange was much larger (86 versus 18%) in the case of the sample with larger surface area. The adsorption kinetics followed a pseudo-second-order model and the equilibrium data were correlated with the Freundlich isotherm.     

Solution combustion synthesis of cerium oxide nanoparticles as corrosion inhibitor

In this study, combustion synthesis of cerium oxide nanoparticles was reported using cerium nitrate hexahydrate as starting material as well as urea, glycine, glucose, and citric acid as fuels. The influence of fuel type on structure, microstructure, band gap, and corrosion inhibition was investigated. X-ray diffraction (XRD) patterns and scanning electron microscopy micrographs showed that CeO₂ nanoparticles with different morphologies were obtained depending on the fuel type. Microstructural changes from unreacted gel to sponge-like morphologies were resulted by varying the fuel type from urea, glycine, and glucose to citric acid. In addition to Ce–O bonds, Fourier transform infrared analysis showed carbon bonds of carbonaceous compositions from incomplete combustion which were declined during combustion reaction. Furthermore, corrosion analyses showed that samples synthesized using urea fuel released the most Ce⁺⁴ ions and could have better protection than other samples.     

燃烧合成钛酸钡粉体的研究进展

近年来，高纯超细钛酸钡粉体的制备技术发展十分迅速，它们在钛酸钡电子陶瓷的应用研究中起着日益重要的作用。燃烧法制备陶瓷粉体是一种新型的材料合成工艺技术，有其独特的优点和特点。简要回顾了燃烧法合成的历史，对燃烧法合成无机粉体现有工艺做了新的分类和介绍，最后就燃烧合成钛酸钡粉体的制备技术做了综述。     

微波辅助溶液燃烧法制备MgAl_2O_4粉体

将硝酸镁、硝酸铝、尿素按物质的量比为1 2 6.66制得透明混合前驱液,用低温燃烧技术与微波加热技术相结合的方法制备了高纯度、低团聚的镁铝尖晶石(MgAl2O4)粉体。研究了燃烧反应过程中,微波输出功率(200、400、600、700 W)对Mg Al2O4粉体晶体结构、形貌及比表面积的影响。结果表明:微波高效加热方式导致燃烧反应瞬间产生大量气体,促进了Mg Al2O4超细颗粒的形成。同时,随着微波输出功率的增加,尿素氧化加速,利于MgAl2O4晶粒的生长发育。在微波功率700W,微波时间2 min的条件下,可制备结晶完整,粒度分布均匀(平均晶粒尺寸为56.03 nm)的Mg Al2O4粉体。     

Solution combustion synthesis (SCS) of chrome alumina as a high temperature pink pigment

In this article, one step synthesis of the chrome alumina pink pigments is investigated. Results indicated that adjusting ignition parameters such as the fuel type (glycine, citric acid, and urea) and the oxidizer to fuel ratio, is the essential factor to obtain the straight corundum structure of the pigment. According to this, chrome alumina pink pigment was just synthesized by the urea fuel in 1.8 oxidizer to fuel (O/F) ratio. The effect of ignition parameters on the morphology was also studied. The microstructure was changed from ultra‐fine irregular agglomerates to sponge‐like flakes by the change in the fuel type from citric acid to urea. Colorimetric characteristics confirmed the relationship between the formation of the corundum structure and one step synthesis of the pink pigment. The pink color of synthesized pigments was comparable with commercial purplish pink pigments of tiles.     

An investigation of fuel precursors and calcination temperature to obtain mayenite (Ca12Al14O33) powders by solution combustion synthesis

The influence of the fuel (glycine, urea, citric acid and sucrose) and calcination temperature used to obtain calcium aluminate in the mayenite phase assisted by solution combustion synthesis (SCS) is the central point of this work. Thermal gravimetric analysis helps to establish the calcination temperatures used (1100, 1200 and 1300 °C). Using the X-ray diffraction technique (XRD) and complementary analyses, such as Raman spectroscopy, the specific surface area and laser granulometry, it was possible to elucidate the behavior and relationship of the fuel and heat treatment on the phase formation, crystallite size and powder crystallinity. Glycine showed better performance than other fuels, with the lowest calcination temperature, obtaining pure mayenite with nanometric crystallite size in all calcination ranges. Thus, it was observed that the type of fuel has an influence on obtaining pure mayenite, as well as the calcination temperature, and glycine reveals the best performance.     

Solution combustion synthesis of nanostructured iron oxides with controllable morphology,composition and electrochemical performance

Nanostructured iron oxides have emerged as promising materials for electrochemical energy storage and conversion devices due to their high theoretical capacity, eco-friendliness and earth abundance. Particularly, the morphology- and composition-controllable synthesis of nanostructured iron oxides is extremely important to optimize their electrochemical performance. However, the development of facile and effective synthetic method is still a great challenge. In this paper, we demonstrated a one-pot solution combustion synthesis (SCS) approach for the time- and energy-effective preparation of nanostructured iron oxides with controllable morphology and composition just by tuning the molar ratio (φ) of fuel (glycine) to oxidizer (ferric nitrate). Innovatively, the effects of φ value on the control of combustion reaction mechanism, morphology and composition of SCS products, and the electrochemical properties in relation to the morphology and composition have been systematically investigated. The results revealed that with the increase of φ value, the reaction mechanism varied from pyrolysis to combustion and the combustion phenomenon changed from volumetric mode to self-propagating mode. Correspondingly, the morphology of products evolved from uniform nanoneedles to porous nanosheets, and finally into aggregated nanoparticles. Meanwhile, the phase composition of these products changed from amorphous α-Fe₂O₃ to crystalline α-Fe₂O₃, and eventually into α-Fe₂O₃/Fe₃O₄ composites. When evaluated as lithium ion battery anode, the as-prepared α-Fe₂O₃/Fe₃O₄ porous nanosheets (φ = 1.0 product) exhibited the best electrochemical properties (a high reversible capacity of ~ 1200 mA h g^?1 and an excellent rate capability) among all the SCS products, which may be attributed to its mesoporous structure (supply favorable accessibility for electrons), nanosheet morphology (shorten the transport length of Li⁺) and appropriate proportion of Fe₃O₄ phase (enhance the electronic conductivity). Consequently, the facile SCS method demonstrated here might provide a new methodology for the morphology and composition-controllable synthesis of nanomaterials, for which a number of prospective applications in electrochemical fields can be envisioned.     

Combustion synthesis and characterization of Sr3Al2O6

In this paper, the synthesis by solution combustion (SCS) of tri-strontium aluminates (Sr₃Al₂O₆), using different fuel amounts, has been studied. The main objective was to understand the effect of the amount of fuel on phase formation, yield and purity of the product using urea as fuel. The combustion temperatures of each reaction were followed by digital pyrometry. Phase compositions were determined by X-ray diffraction (XRD). The microstructural characteristics during the SCS process were studied by field emission scanning electron microscopy (FESEM). The specific surface area was calculated with the BET model from adsorption data. The results showed that the Sr₃Al₂O₆ was the main phase obtained in all syntheses. This aluminate with high content of Sr is considered attractive for use in applications requiring radiopacity as biomaterials for dental and bone repair. The maximum measured temperature during synthesis, with excess fuel, was approximately 987°C. It was higher than that obtained in the case of using stoichiometric amounts of fuel which was 762°C. The product obtained in this second case had a submicrometer structure, with highly crystalline particles and a specific surface of 0.21 m²/g. It was higher than that obtained with excess of fuel (0.07 m²/g).     

Molten-salt-assisted combustion synthesis of B4C powders: Synthesis mechanism and dielectric and electromagnetic wave absorbing properties

A novel electromagnetic wave (EMW) absorber was prepared by combustion synthesis. Boron carbide (B₄C) powders with different grain sizes using a molten-salt-assisted combustion technique with B₂O₃, CB (carbon black), and Mg powders as starting materials, and NaCl as an additives. The effects of the NaCl content on the phase compositions and the microstructure of the products were characterized. A combustion front quenching method was used to elucidate the mechanism for the B₄C powders synthesis. The dielectric, and EMW absorbing properties in the X-band were also investigated. The results showed that the addition of NaCl significantly reduced the grain size of B₄C powders. Nanoscale B₄C powders with cubic polyhedral structures were synthesized using 6 wt% NaCl (labeled as N-6). According to the quenching test results can be obtained that the first step in the combustion synthesis was melting B₂O₃ into a glassy substance. At the same time, Mg melted and formed a liquid pool into which the NaCl dissolved, followed reduction of the B₂O₃ to B. The formed B eventually reacted with CB to form B₄C, and the B₄C particles precipitated from the matrices. The N-6 sample exhibits optimal dielectric and EMW absorbing properties, because of a high specific surface area that enhances interfacial and space charge polarization.